The hydrolysis capability of polymer organic compounds is one of astonishing performances given to microorganisms in the nature. Microorganisms readily perform the reaction in a quite natural environment of normal temperature and pressure, thus breaking the organic molecular chain to decrease the molecular weight of the organic compound. The method is the one acquired and improved by microorganisms during a long period of several hundreds of millions of years, and is normally called the “method of hydrolysis by enzymes”.
The method of hydrolysis by enzymes is difficult for human to follow, at least at present, even with the total human intellectual power. The decomposition products of the “method of hydrolysis by enzymes”, or the resulting substances of decomposition given by microorganisms, become useful components for all the other living things, and they are the basic elements which can be absorbed by the living things to become tissue thereof.
Although the method of hydrolysis by enzymes is difficult for human to follow, at present, there is one method to obtain the same result thereto using a method other than the method of hydrolysis by enzymes. The method is the “method of hydrolysis using physical energy”. The method inherently resembles the phenomenon of decomposition by geothermal water erupted from earth interior at the bottom of deep sea, or at several thousands of meters below the sea level. According to the method, the reaction proceeds in a state far beyond the water critical condition of both temperature and pressure, (375° C. and 220 atm). As the result of the reaction, organic compounds can be hydrolyzed, many kinds of substances (compounds) including metals can be decomposed, and the structural components of substances can be eluted.
The hydrolysis can be applied also when that high pressure and high temperature condition is brought into a more practical state (to a state more close to normal temperature). In particular, when organic matter is placed at a state exceeding 100° C. and 1 atom, the organic matter is gradually hydrolyzed with time. Consequently, the result of the “method of hydrolysis using physical energy” becomes equivalent to the result of the “method of hydrolysis by enzymes” executed by microorganisms. There are introduced methods for decomposing biodegradable plastics and the like utilizing the principle: for example, Patent Document 1 discloses the method of utilizing supercritical hot-water treatment, and Patent Document 2 discloses the method of utilizing hot water in subcritical state.
Not limiting to the reaction examples in supercritical state and subcritical state, generally there occurs phase transition of substances under high pressures even at relatively low temperatures owing to the influence of partial pressure ratio. For the case of organic matter, however, there is a risk of carbonization if the pressure is higher than the saturation water vapor pressure even at a relatively low temperature, and of liquefaction and inclusion of solvent and the like if the temperature is lower than that of saturation water vapor pressure. Therefore, actual and effective utilization of the “method of hydrolysis using physical energy” is difficult to establish the treatment conditions including temperature and pressure.
That is, for utilizing the supercritical fluid and the subcritical fluid in the treatment, there is required a treatment apparatus that generates an extremely high temperature and pressure condition, and that maintains the generated temperature and pressure condition. Generally the apparatus to maintain high temperature and high pressure state becomes difficult in fabrication with increase in the capacity thereof, and the fabrication cost remarkably increases with increase in the capacity thereof, thus the application to large scale industrial facilities is difficult. Furthermore, the extremely high decomposition capability of supercritical hot water and subcritical hot water affects not only the target organic matter for treatment but also the treatment vessel, which requires to use expensive materials to the apparatus to prevent decomposition of the treatment vessel.
Among the synthetic resins having ester bond in the composition structure thereof, polylactic acid products receive specifically high social expectation, thus they have begun to be used in many fields in recent years. They have, however, basic problems of long molding cycle, of inferiority in the characteristic of thermal resistance of the produced molded articles, and further in the mechanical characteristics (toughness, impact resistance, and the like) compared with those of existing synthetic resin molded articles.
To solve the problems, there were generally given many countermeasures, including mixing the polylactic acid with other existing synthetic resins, and mixing various kinds of substances as filler, thus the polylactic acid products have been entering practical applications. On actual use of the polylactic acid as the material of the products, solvent, coloring pigment, and the like are blended therein, thus normally the products contain many kinds of coexisting substances.
The most efficient and desired reclaim to reuse of the polylactic acid products after use is to recycle thereof by recovering the used polylactic acid products to the raw material of the polylactic acid products. In view of utilization as the raw material of the polylactic acid products, it is natural to desire to bring back to high purity lactic acid raw material. However, reuse of the polylactic acid products is difficult.
Patent Document 1: Japanese Patent Laid-Open No. 11-292777
Patent Document 2: Japanese Patent Laid-Open No. 2003-313283